This invention relates to hydraulic apparatus. The invention is described hereinafter with particular reference to a hydraulic cylinder and piston assembly which is suitable for use in the brake system of a motor vehicle, but the invention is not confined to this particular application.
Despite the widespread use of disc brakes, many vehicles still make use of drum brakes. There are a number of reasons for this which are not necessary for an understanding of the invention. Drum brakes function adequately but require adjustment at regular intervals as the brake shoes wear. Adjustment is particularly necessary when a hand brake which acts on the brake shoes is incorporated in the system. A hydraulic brake circuit which is actuated by pressure applied by the driver's foot can normally take up a fair degree of play to compensate for worn brake shoes but for effective hand brake operation the play caused by worn brake shoes must be compensated for.
A variety of techniques and devices, described for example in the specifications of South African patent No.75/4532, U.K. patent No.2168770 and U.S. Pat. No. 4,056,175 have been used to make it possible to compensate for worn brake shoes, sometimes automatically. Some of these devices are however complex, or require a substantial re-design of the existing brake actuating mechanism.